The National Cancer Institute Organ Systems Program-sponsored Upper Aerodigestive Cancer Task Force workshops are specifically designed to enhance interactions between basic science and clinical investigators and between academic institutions and the community, and ultimately will contribute to more expeditious clinical advances. The third workshop in this series focused on the rapidly expanding area of chemoprevention of upper aerodigestive epithelial cancers. The first two sessions were devoted to discussion of in vitro and animal-model data documenting the multistep process of squamous differentiation and carcinogenesis, associated molecular and biochemical alterations, and modulation by chemopreventive agents. Animal-model studies have identified several promising chemopreventive agents and synergistic combinations for clinical trial. The last two sessions reviewed nutritional epidemiology, major methodologic issues of large intervention studies, and the novel concept of biologic markers as intermediate endpoints for chemoprevention trials.